In recent years, avian influenza infection in humans has been reported with concern that much damage is caused by infectious human-to-human pandemic outbreak. Therefore, there have been being built, in the world, stockpiles of a pandemic vaccine that would have the high possibility of being effective against the avian influenza. In order to administer the pandemic vaccine to many people, studies have been made on the increasing amount of production of the vaccine.
The skin is made up of three layers including the epidermis, the dermis and the subcutis. The epidermis is a layer of about 50 to 200 μm from the skin surface, and the dermis is a layer of about 1.5 to 3.5 mm contiguous to the epidermis. Generally, an influenza vaccine is subcutaneously or intramuscularly administered, for which it is administered in the lower section of the skin or in a deeper section.
On the other hand, it has been reported that when an influenza vaccine is administered in the upper layer of skin, as a target site, wherein immunocompetent cells exist abundantly, there can be obtained the capability of immune acquisition equal to that attained by subcutaneous or intramuscular administration if the amount of administration is reduced (Non-Patent Document 1). Accordingly, since the amount of administration can be reduced by administration of a pre-pandemic vaccine in the upper layer of skin, the amount of administration can be reduced and thus, the pre-pandemic vaccine can be administered to a greater number of people. It will be noted that the upper layer of skin indicates the epidermis and dermis of the skin.
For the administration of a drug in the upper layer of skin, there have been reported a number of methods making use of a single needle, a multistylus, a patch, a gas and the like. It has been accepted that when taking into account the stability and reliability of administration and the production cost, the method using a single needle is most suited as a method of administration in the upper layer of skin. For the method of administering a vaccine in the upper layer of skin by use of a single needle, the Mantoux method is known from long ago. The Mantoux method is one wherein a needle having a size of 26 to 27 gauge and a short bevel needle tip is generally inserted to a depth of about 2 to 5 mm from an inclined direction of about 0 to 15° relative to the skin so as to administer about 100 μl of a drug.
The administration procedure of a drug based on the Mantoux method is difficult, with its success rate being entrusted to the skill of a doctor who makes an injection. Especially, children are apt to act up upon administration and thus, it has been difficult to administer an influenza vaccine according to the Mantoux method. Hence, there has been demanded the development of a device, with which a vaccine can be simply administered in the upper layer of skin.
In Patent Document 1, there is described an injection device wherein a limiter having a skin contact surface is connected to a hub of a syringe. The limiter of the injection device set out in this Patent Document 1 is tubularly formed to cover around a needle tube and has a skin contact surface from which an injection needle projects. With this limiter, the length of the injection needle projecting from the skin contact surface (projection length) is regulated at 0.5 to 3.0 mm, under which a drug injected from the injection needle is administered in the skin.